1. Field of the Invention
This invention relates to techniques for minimizing the evaporative losses of stored hydrocarbons. In particular, the present invention is concerned with suppressing the volatilization of hydrocarbons contained in petroleum products such as crude oil.
2. Background of the Invention
In the past, petroleum products, particularly crude oil, have been relatively inexpensive commodities with the result that conservation of these commodities was never of great consequence. In very recent years, however, increased world demand for all natural resources has subsignificantly altered the prior supply demand relationships so that losses of hydrocarbons from evaporation is deemed quite serious, not only from an environmental point of view but also from a conservation point of view. Indeed, this concern for preserving our natural resources applies not only to petroleum hydrocarbons but to all volatile liquids.
In the description to follow, reference will be made primarily to suppressing the loss of hydrocarbons by vaporization from crude oils; however, it is to be understood that crude oil is merely one example of a hydrocarbon which contains sufficient amounts of volatile components which will undergo vaporization in substantial amounts during storage.
As will be appreciated, crude oil contains a very wide spectrum of hydrocarbons ranging from those which have very high boiling points to those which would exist in the vapor state if they were isolated. Indeed, it is the presence of these latter materials that contributes to the significant vapor pressure of crude oil.
There have been a number of techniques suggested in the past for inhibiting the vaporization of hydrocarbons. For example, in U.S. Pat. No. 1,985,491, it is suggested that a fatty acid soap be mixed with water and then beat into a froth with a vigorous air blast. The froth, thereafter, is spread on the surface of oil, so as to minimize evaporation and oxidation of the oil.
In U.S. Pat. No. 2,822,238 evaporation of volatile nonaqueous liquid products is retarded by floating small hollow particles, wet by water, on the surface of the volatile liquid.
In U.S. Pat. No. 2,907,627, a technique is disclosed for inhibiting vapor loss by spreading a synthetic resin plastic such as a polyurethane on the surface of the crude petroleum. In contrast, thereto, U.S. Pat. No. 3,421,838 discloses the use of rubber cement as a vapor barrier for volatile petroleum products.
Other techniques suggested, inhibiting vaporization of hydrocarbon materials include the use of a gelling material to create an integral roof on an oil tank. In this regard see U.S. Pat. No. 3,639,258. Mention should be made also of the technique of preventing hydrocarbon losses during the loading of vessels by use of an aqueous foam which is stable during the period corresponding to that required for loading. For this technique, see U.S. Pat. No. 3,850,206. These last two techniques for inhibiting vaporization of hydrocarbons have more limited applicability than the above-mentioned techniques. Moreover, there still remains a need for simple, inexpensive and widely applicable techniques for inhibiting the loss of vapor from petroleum hydrocarbons.